This study aims to examine the mediating role of social media marketing effectiveness in the relationship between customer engagement dimensions (cognitive, emotional, behavioral, transactional, and social) and brand loyalty in the context of Amazon as a retail brand store. A quantitative approach was adopted, employing a survey-based method to collect data from 320 consumers who engage with Amazon as a retail brand store on social media platforms. Findings reveal positive effects of cognitive, emotional, transactional, and social engagement on brand loyalty and social media marketing effectiveness. However, behavioral engagement exhibited a negative impact. Social media marketing effectiveness positively influenced brand loyalty and mediated the relationships between customer engagement dimensions and brand loyalty. This study contributes to literature by challenging assumptions and providing insights into the interplay among customer engagement dimensions, social media marketing effectiveness, and brand loyalty. This offers brands the opportunity to promote and increase their awareness with the use of social media to interact with existing customer base that will boost loyalty in the long run. Only a few studies have examined social media marketing effectiveness as a mediator between customer engagement dimensions and brand loyalty. Therefore, this work endeavors to fill this gap by investigating consumer engagement, social media marketing and brand loyalty in an age when the internet plays an important role.